The valuables were part of a HK$100 million haul – 18 diamonds, three rings and US$8,600 in cash – taken from a safe in the office of M&B Diamonds in Central on Thursday afternoon.

According to authorities, the suspect posed as a jewellery buyer and contacted the company’s Israeli owner through Instagram before coming to Hong Kong from the Middle East on Wednesday.

Police said the man visited the office on the 16th floor of Winway Building on Wellington Street twice on Thursday morning to scout the premises.

He returned at 2pm, when two female employees were there. He attacked one of the women, 38, shortly after her colleague went out for lunch.

Officers said it seemed the woman was beaten unconscious after she refused to reveal the password.

Shortly before 2.30pm, the man found a key to open the safe but, in trying to open it, triggered the security system which locked the door to the premises. That system alerted a security company, which called police.

“He failed to unlock the front door and, as he heard someone trying to open it from outside, he swallowed part of the haul with water behind the reception counter, before hiding in a store room,” another source said.

Police and the company’s 32-year-old Israeli owner arrived to find the woman unconscious in one of the rooms.

“The suspect pretended to be unconscious when he was found inside the store room,” the source said.

Eight diamonds, valued at US$5.4 million, were found on him along with the US$8,600 in cash.